1 in the design of IO mechanism, two important goals: efficiency and versatility.
Efficiency is important because IO operations typically a computer system bottleneck.
GM: For simplicity and to avoid the wrong reason, it is desirable to use a unified approach to deal with all devices. Both show unity: 1) Processor look at the way IO device
2) the way the operating system management and operation of the IO IO devices
Currently uses a hierarchical, modular approach to design IO functions, it hides most of the details of the underlying IO devices, enabling users to process and high-level operating systems can read, write, open, close, lock and unlock other common functions to operate IO device.
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